Contemporary physics seem to indicate that there are good reasons, theoretically and physically, for an idea that there is a plurality of worlds.  This concept has come to be understood as the multiverse.  The multiverse is not monolithic but it is modeled after the contemporary understanding of an inflationary model of the beginning of this universe.  Max Tegmark has championed the most prominent versions of the multiverse.[1]  Tegmark has made a four-way distinction.

Tegmark’s first version of the multiverse is called the level one multiverse.  The level one is, for the most part, more space beyond the observable universe.  So, theoretically, if we were to go to the “edge” of the universe there would be more space.  Having this model as a version of the multiverse may be misleading because there is still only one volume, landscape, or system involved.  A generic prediction of cosmological inflation is an infinite space, which contains Hubble volumes (what we see in our universe) realizing in all conditions—including an identical copy of each of us about 10^10^29 meters away.[2]